Power-distribution networks typically deliver electrical power to consumers using an interconnected arrangement of transmission lines, distribution buses, distribution feeders, etc. Power-distribution networks are typically configured so that electrical power can be delivered over more than one path within the network. Moreover, power-distribution networks are often configured so that power can be delivered from two or more alternative sources (although only one source can supply the network at a given instant). Configuring a power-distribution network in this manner reduces the potential for a single-point fault to leave large numbers of users without electrical power.
Power-distribution networks are commonly equipped with sectionalizers that permit a section of the network to be isolated from its neighboring sections on a selective basis. The feature permits a faulted section of the network, i.e., a section of the network having a fault therein, to be de-energized and isolated so that other sections of the network can be re-energized after the occurrence of the fault.
Power-distribution networks are also commonly equipped with reclosers. Reclosers are adapted to trip, or open, in response to an overcurrent condition, thereby interrupting the flow of electrical power and clearing the fault condition on at least a temporary basis. A typical recloser is also adapted to close after a predetermined interval to restore the flow of electrical power to the network. A reoccurrence of the fault upon closing will cause the recloser to once again trip. Transient-type faults can sometimes be cleared by repeated closings and openings of the recloser. Hence, the recloser may be closed several times following each trip until the fault clears, or until a predetermined number of closings have occurred. Reclosers can thus eliminate prolonged power outages and unnecessary service calls caused by a transient fault.
The reclosers and sectionalizers of a power-distribution network can be connected to a centralized communication unit that facilitates communication between the reclosers and sectionalizers. This feature permits the reclosers and sectionalizers to share operational information, via the communication unit, such as open-closed status, load condition, etc. The reclosers and sectionalizers can thus be adapted to operate in a coordinated manner, i.e., each recloser and sectionalizer can be adapted to open or close itself based on the operational status of the other reclosers or sectionalizers. Coordinating the operation of the reclosers and sectionalizers in this manner permits faulted sections of the power distribution network to be isolated, and allows power to be restored to sections in which a fault is not present (provided an alternative power source is available).
Power-distribution networks that are not equipped with a centralized communication unit often rely on repeated closings and openings of a recloser to identify and isolate a faulted section. For example, the sectionalizers downstream of the recloser, i.e., the sectionalizers separated from the voltage source by the recloser, may be opened on a sequential basis after the recloser has cycled through a predetermined number of closings and openings. More particularly, the sectionalizer located farthest from the recloser in the network may be adapted to open after the recloser has closed and reopened a predetermined number of times, e.g., two (this can be accomplished by programming the sectionalizer to open after a predetermined amount of time has elapsed following a drop in the voltage or current in the sectionalizer).
The sectionalizer located immediately upstream of the open sectionalizer may be adapted to open after the next closing and reopening the recloser. This process occurs for each subsequent upstream sectionalizer until the recloser remains closed, i.e., until the faulted section is no longer energized upon the closing of the recloser. This approach is time consuming in comparison to the use of a centralized communication unit to facilitate coordinated operation among the reclosers and sectionalizers. Moreover, power cannot be restored to un-faulted sections located downstream of the faulted section, i.e., to un-faulted sections separated from the voltage source by the faulted section, using this approach.
A centralized communication unit, however, represents an additional component in the power-distribution network, and thus adds to the overall cost, complexity, and maintenance requirements of the network. Moreover, the lines through which communications are exchanged between the centralized communication unit and the other components of the power-distribution network add further to the overall cost, complexity, and maintenance requirements of the network. Also, the centralized communication unit and its associated communication lines represent potential points of failure that can adversely affect the operation of the power-distribution network.